1. Field of the Invention
This invention concerns the use of reservoir conditioning agents in the course of a chemical flooding operation within a subterranean petroleum reservoir.
2. Description of the Prior Art
The crude oil which is accumulated in subterranean reservoirs is recovered or produced through one or more wells drilled into the reservoir. Initial production of the crude oil is accomplished by "primary recovery" techniques wherein only the natural forces present in the reservoir are utilized to produce the oil. However, upon depletion of these natural forces and determination of primary recovery a large portion of the crude oil remains trapped within the reservoir. Also many reservoirs lack sufficient natural forces to be produced by primary methods from the very beginning. Recognition of these facts has led to the development and use of many enhanced oil recovery techniques. Most of these techniques involve injection of at least one fluid into the reservoir to produce an additional amount of the crude oil therefrom. Some of the more common methods are water flooding, steam flooding, miscible flooding, CO.sub.2 flooding, polymer flooding, surfactant flooding, caustic flooding and in situ combustion.
Water flooding which involves injection of water into the subterranean oil reservoir for the purpose of displacing the crude oil from the pore spaces of the reservoir rock toward the producing wells is the most economical and widely used of the enhanced oil recovery methods. Nevertheless water does not displace oil with high efficiency because of the immiscibility of oil and water and because of the resulting high interfacial tension between them.
Surfactant flooding involves the addition of one or more surface active agents or surfactants to the water flood for the purpose of minimizing the waterflooding problems mentioned above. Research in this area has produced a variety of effective surfactant compounds for use in petroleum recovery operations. For example, U.S. Pat. No. 3,468,377 discloses the use of petroleum sulfonates in waterflooding operations and U.S. Pat. No. 3,553,130 discloses the use of ethylene oxide adducts of alkyl phenols for the same purpose. The use in waterflooding operations of water-soluble surface active alkylene earth resistant polyglycol ethers is disclosed in U.S. Pat. No. 2,233,381. Other specialized surfactants, as will be discussed later, have been discovered to have special properties useful in waterflooding operations such as a tolerance for high salinity and diavalent ion concentrations often found in reservoir waters.
However, field operations employing surfactants and surface active agents in injected aqueous fluids have not always been entirely satisfactory due to the fact that these materials are often retained within the formation matrices to a relatively high degree resulting in an ever declining concentration of the surfactant materials as they progress through the reservoir. As a result large concentrations of surface active materials have heretofor been necessary to maintain a sufficient concentration at the oil water interface. Therefore, large quantities of these surfactant materials are usually required and due to the high cost of these materials the economic valuability of the surfactant flooding project is adversely effected.
This chemical retention phenomenon has been recognized by those skilled in the art of oil recovery and the use of certain "sacrificial compounds" has been disclosed for injection into the subterranean petroleum reservoir to reduce the amount of chemical retention therein. For example, U.S. Pat. No. 3,424,054 discloses the use of aqueous solutions of pyridine, U.S. Pat. No. 3,469,630 discloses the use of sodium carbonate and inorganic poly- phosphates and U.S. Pat. No. 3,437,141 discloses the use of soluble carbonates, inorganic polyphosphates and sodium borate in combination with a saline solution of a surfactant having both high and low molecular weight components. The use of aqueous lignosulfonate solutions as sacrificial components has been disclosed in U.S. Pat. Nos. 3,384,171, 3,700,031 and 4,157,115.